319 research outputs found
Functional biomarkers for monitoring propylene glicol degrading bacteria in contaminated sites
No full textSelezione di colture batteriche degradanti POP e loro monitoraggio in processi di bioarricchimento di suoli
No full textCaratterizzazione di popolazioni microbiche capaci di utilizzare inquinanti organici poco solubili in fase acquosa (NAPL)
No full textArsenic resistant bacteria isolated from agricultural soils of Bangladesh and characterization of arsenate reducing strains
No full textAims:
To analyse the arsenic-resistant bacterial communities of two agricultural soils of Bangladesh, to isolate arsenic-resistant bacteria, to study their potential role in arsenic transformation and to investigate the genetic determinants for arsenic resistance among the isolates.
Methods and Results:
Enrichment cultures were performed in a minimal medium in the presence of As(III) and As(V) to isolate resistant bacteria. Twenty-one arsenic-resistant bacteria belonging to different genera of Gram-positive and Gram-negative bacteria were isolated. The isolates, with the exception of Oceanimonas doudoroffii Dhal Rw, reduced 2 mmol l−1 As(V) completely to As(III) in aerobic conditions. Putative gene fragments for arsenite efflux pumps were amplified in isolates from Dhal soil and a putative arsenate reductase gene fragment was amplified from a Bacillus sp. from Rice soil.
Conclusions:
Phylogenetically diverse arsenic-resistant bacteria present in agricultural soils of Bangladesh are capable of reducing arsenate to arsenite under aerobic conditions apparently for detoxification purpose.
Significance and Impact of the Study:
This study provides results on identification, levels of arsenic resistance and reduction of arsenate by the bacterial isolates which could play an important role in arsenic cycling in the two arsenic-contaminated soils in Bangladesh
Removal of arsenic from contaminated groundwater by goethite adsorption in the presence of the arsenite-oxidizing bacterium Aliihoeflea sp. strain 2WW
No full textContamination of aquifers with As has raised great concern, because of serious risks to human health. The revised drinking water standard for arsenic imposes a 10 μg L-1 threshold limit, which has boosted research efforts to remove As efficiently. Arsenic has a high affinity for adsorption to metal oxides, with As(V) being more effectively adsorbed than As(III). Consequently the oxidation of As(III) to As(V) is a prerequisite for achieving As concentrations below the threshold. Bio-oxidation of As(III) by microorganisms has recently received attention as a sustainable alternative to the use of chemical oxidants.
The aim of our work was to improve the removal of As from groundwater by oxidizing As(III) to As(V) followed by adsorption to goethite. For this purpose, we first isolated an arsenite-oxidizing bacterium, Aliihoeflea sp. strain 2WW, from a biofilm treating contaminated groundwater, and subsequently investigated the As(III) oxidation capability of this strain. The experiments were conducted in Tris-HCl 5 mM (pH 7.2) containing 200 μg L-1 of As, using As(III)-induced and non-induced resting cells. As(III) and As(V) adsorption capability of goethite was evaluated by using 4 g L-1 goethite and increasing As concentrations (25-800 μg L-1). Finally we tested the As-removal efficiency of the combined 2WW-goethite system on a synthetic contaminated water and a contaminated groundwater sample. Resting cells of an As(III)-induced culture of 2WW were able to oxidize completely 200 μg L-1 of As in 8 hours, while non-induced cells oxidized As in 24 hours. Subsequently, results from the As-adsorption experiments showed that goethite removed almost the complete 200 μg L-1 of As(V) from the solution, while for As(III) only 75% was adsorbed.
Our results indicate that As(III) oxidation by Aliihoeflea sp. strain 2WW combined with goethite adsorption is an efficient approach for the removal of As from contaminated groundwater.
Research funded by CARIPLO Foundation-2010-2221
Does fluoroscopy induce DNA oxidative damage in patients undergoing catheter ablation?
No full textDemographic, clinical and laboratory features of the cohort
Effect of environmental stresses on plant grow promoting characteristics of the arsenite oxidizer Pseudomonas sp. strain N2
No full textHeavy metals resistant bacteria with plant growth-promoting (PGP) characteristics can be used to facilitate the proliferation of plants under environmentally stressful conditions, such as drought, salinity and heavy metals contamination. Moreover, arsenic-transforming PGP bacteria, influencing arsenic mobilization in soil, can enhance arsenic uptake by plant.
The aims of this study were: (i) to characterize an arsenic-resistant Pseudomonas sp. strain N2 for resistance to osmotic stresses, production of stress-related phytohormones, PGP traits and arsenic transformation, and (ii) to evaluate the effect of arsenic on these characteristics.The capability to respond to osmotic stresses (-1.5 MPa) was evaluated by measuring the bacterial growth in LB medium separately added of: 175 mmol/L of Na3AsO4, 400 mmol/L of NaCl, or 26% (w/v) PEG6000 (Sosa et al., 2005). Production of stress-related phytohormones (indole acetic acid IAA, and jasmonic acid, JA) was determined in yeast mannitol medium (YEM) in the absence and in the presence of arsenate (50 mmol/L), arsenite (3 mmol/L), and PEG6000 (13.7% w/v), as stress agents. Tested PGP characteristics were: the ability to grow on 1-aminocyclopropane-1-carboxylic acid (ACC) as sole nitrogen source, the production of siderophores and proteolitic, chitinase and phosphate solubilising activities. Phosphate solubilisation activity was evaluated in YEM with Ca3(PO4)2 (5 g/L) in the absence or in the presence of arsenite or arsenate. Arsenic transforming capabilities were evaluated during 72 h growth in Tris Mineral Medium (Mergey et al., 1985) supplemented with 0.6% (w/v) gluconate (TMMG) spiked with 3 mmol/L of arsenite or arsenate.
Strain N2 was able to tolerate -1.5 MPa: osmotic stress generated by the presence of arsenic was tolerated better than those generated by NaCl and PEG6000. The strain was able to produce 68 pmol/ml of IAA and 0.18 pmol/ml of JA and to solubilise 100 mg/L phosphate. While the production of IAA was enhanced by the presence of arsenic forms it was not affected by osmotic stress. On the contrary, phosphate solubilization was impaired by arsenic. Strain N2 possessed all the tested PGP characteristics and it completely oxidized arsenite to arsenate, while it did not reduce arsenate.
Our results suggest that strain N2 possesses PGP characteristics not affected by the presence of arsenic and of osmotic stresses. Moreover, the ability to solubilize phosphate may contribute to improve plants’ phosphorous nutrition. Pseudomonas sp. strain N2 might be a candidate inoculum useful to amplify plant resistance in stress conditions.
Acknowledgments
Funding for this work was provided by: Fondazione CARIPLO (project 2010-2221) and PRIN (project 2010JBNLJ7_004)
Contributo di batteri PGP arsenico-resistenti nella mobilizzazione e traslocazione in Helianthus annuus (L.)
No full textPerformance of Cd-resistant rhizobacteria to improve Brassica napus growth under cadmium stress
No full textCadmium is one of the most toxic heavy metal for plants, inhibiting root and shoot growth and affecting nutrient uptake and homeostasis. Plant growth promoting rhizobacteria (PGPR) can improve plant nutrition and growth, competitiveness and responses to external stress factors.
The plant growth promoting activity of four cadmium-resistant rhizobacteria (Pseudomonas tolaasii ACC23, Pseudomonas fluorescens ACC9, Alcaligenes sp. ZN4 and Mycobacterium sp. ACC14) with multiple PGP traits was assessed on canola (Brassica napus) in presence and in absence of Cd. The considered PGP traits were the production of indole acetic acid (IAA) and siderophores and the capability of consuming 1-aminocyclopropane-1-carboxylate (ACC), the immediate precursor of ethylene. All the studied strains had in vitro ACC deaminase (ACCD) activity. The strains produced IAA and siderophores more actively under Cd-stress and the ACCD activity of only two strains was reduced by the metal. Root elongation assay conducted on B. napus under gnotobiotic conditions demonstrated significant increases in root elongation of inoculated canola seedlings grown in the presence or in the absence of cadmium (from 21 to 104% and from 34 to 97%, respectively ) compared to the control plants. The pot culture experiment with treated (15 g Cd2+ g-1 dw) and un-treated soil clearly demonstrated the beneficial effects of the inoculations with P. tolaasii ACC23, P. fluorescens ACC9 and Mycobacterium sp. ACC14.
The PGPR protected plants from growth inhibition caused by the metal, as demonstrated by dry-weight biomass data, without influencing the specific accumulation of cadmium in root and shoot systems. However, total Cd uptake per plant significantly increased, thus resulting in a higher metal removal. In particular, the maximum growth and Cd uptake were obtained with P. tolaasii ACC23 and P. fluorescens ACC9.
The isolated bacteria c as inoculants to improve B. napus growth in the presence of toxic concentration of cadmium. Field experiment will confirm the PREP activity of the strains on plant growth in order to stabilize, revegetate and remediate metal-polluted soils
Isolation and characterization of arsenic resistant bacteria from arsenic contaminated soils
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